There are two basic types of conventional air cushion vehicles. In the "plenum" type vehicle, the conventional hovercraft generates an air cushion in a large pressurized air plenum chamber under the vehicle surrounded by a depending flexible shirt. Air escapes from beneath the flexible skirt. Lift is maintained by the air pressure in the plenum chamber under the vehicle developed by a blower or propeller fan. Operative pressure containment is effected by the relative ground surface closure of the plenum from below and skirt tension around the sides.
In the "peripheral jet" type vehicle, the air cushion is generated by an annular peripheral jet which develops a high pressure bubble, air pocket or cushion under the center of the craft contained by a high pressure curtain of air. In the peripheral jet air cushion vehicles, the annular jet stream around the undersurface of the vehicle is directed downwardly and inwardly to develop this pressurized pocket of air at the center.
A disadvantage of the conventional designs for both approaches is that the integrity of the air cushion may be lost as the vehicle travels over uneven ground. The skirt of the plenum chamber or the air curtain of the peripheral jet may be opened or diverted permitting escape of air and loss of pressure. Effectively, the air cushion or bubble of air is deflated. Furthermore, flexible and selective control of the ground affect "lift" from the air cushion is not available for trimming the attitude of the craft as a result of, for example an unbalanced load which causes the craft or vehicle to list in one direction. Nor is there adequate provision for low speed maneuverability and directional control. Overall, no automatic independent suspension system has been developed for hovercraft and air cushion vehicles.
The Hart U.S. Pat. No. 3,575,116 describes a peripheral jet gas cushion structure with limited rotation of outer peripheral jet curtain defining members. The pivoting or rotation compensates for variation in pressure over the ground by locally varying the mass flow of curtain gas. A disadvantage of this approach, however, is that basically a single peripheral jet air curtain bubble is developed under the vehicle limiting the flexibility and independent response to uneven terrain.
The Pont et. al. U.S. Pat. No. 3,811,527 describes an air cushion vehicle in which compressed air is variably and differentially distributed to peripheral locations or sections by partition flaps responsive to a manual control lever for varying the lift, attitude or direction. The specification mentions that the flaps may be subject to servo control in response to flight parameters over the ground but no arrangement for automatic response is described.
In the Eggington U.S. Pat. No. 3,174,569, trim control is achieved by a variation in air flow in the air curtain around a single large air cushion in response to ground travel parameters. The single large air cushion limits flexibility of response to ground travel parameters. Bertin et. al. in U.S. Pat. No. 3,414,076 describe multiple cushions bounded by a flexible rubber annulus or ring. However, Bertin et. al. do not describe independent and automatic response to variation in ground effect parameters during travel over variable terrain.
In the Croix-Marie U.S. Pat. No. 3,698,506, trim correction and stabilization are achieved by tilting a spring loaded tilting bearing plate above the air cushion. The tilting of the spring loaded bearing plate above the cushion is intended to compensate for possible variations in the distance between the bearing plate and the ground surface. In the Hart U.S. Pat. No. 3,625,157 the entire gas cushion peripheral jet structure itself extends and retracts relative to the vehicle for tracking over the ground. U.S. Pat. No. 3,587,772 describes multiple fixed peripheral channel "air blasting" lift devices on an air cushion vehicle. There is no disclosure of automatic independent response of the fixed "air blasting" lift devices. Other patents such as the Cockerell U.S. Pat. No. 3,272,271 and the Taylor U.S. Pat. No. 3,240,282 describe peripheral jet or peripheral curtain air cushion vehicles with angularly moving or retractable walls or skirts for establishing a single large peripheral jet curtain and air cushion.